Design of a RC medium voltage divider for on-site calibration

The steps followed in the design of a reference resistive-capacitive divider for on-site calibration on the medium voltage grid are described. The design constraints are defined on the basis of the expected on-site conditions, rated primary and secondary voltage, insulation requirements and accuracy performances. The final set up of the divider is defined by making use of a circuital model. Both the stray parameters of the divider components and the capacitive coupling with the shield, which are estimated through finite element modelling, are included in the model. The electric field distribution between divider and shield is also estimated, taking into account the presence of the insulating medium to identify the electric field hot spots and verify the dielectric strength of the device. The variation of the divider behaviour in a frequency range from power frequency to 100 kHz is found to be within 200 ppm and 2 mrad for the ratio and phase displacement, so making feasible the extension of its use over a quite wide frequency range both as a reference or a measuring transducer.